Compliant interconnects in wafers

ABSTRACT

A microelectronic assembly includes a substrate and an electrically conductive element. The substrate can have a CTE less than 10 ppm/° C., a major surface having a recess not extending through the substrate, and a material having a modulus of elasticity less than 10 GPa disposed within the recess. The electrically conductive element can include a joining portion overlying the recess and extending from an anchor portion supported by the substrate. The joining portion can be at least partially exposed at the major surface for connection to a component external to the microelectronic unit.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 12/962,806, filed Dec. 8, 2010, the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to stacked microelectronic assemblies andmethods of making such assemblies, and to components useful in suchassemblies.

Semiconductor chips are commonly provided as individual, prepackagedunits. A standard chip has a flat, rectangular body with a front surfacehaving contacts connected to the active circuitry of the chip. Eachindividual chip typically is mounted in a package which, in turn, ismounted on a circuit panel such as a printed circuit board and whichconnects the contacts of the chip to conductors of the circuit panel. Inmany conventional designs, the chip package occupies an area of thecircuit panel considerably larger than the area of the chip itself. Asused in this disclosure with reference to a flat chip having a frontsurface, the “area of the chip” should be understood as referring to thearea of the front surface.

In “flip chip” designs, the front surface of the chip confronts asurface of a package substrate, i.e., a chip carrier, and the contactson the chip are bonded directly to contacts of the chip carrier bysolder balls or other connecting elements. In turn, the chip carrier canbe bonded to a circuit panel through terminals overlying the frontsurface of the chip. The “flip chip” design provides a relativelycompact arrangement; each chip occupies an area of the circuit panelequal to or slightly larger than the area of the chip's front surface,such as disclosed, for example, in certain embodiments ofcommonly-assigned U.S. Pat. Nos. 5,148,265, 5,148,266, and 5,679,977,the disclosures of which are incorporated herein by reference.

Besides minimizing the planar area of the circuit panel occupied bymicroelectronic assembly, it is also desirable to produce a chip packagethat presents a low overall height or dimension perpendicular to theplane of the circuit panel. Such thin microelectronic packages allow forplacement of a circuit panel having the packages mounted therein inclose proximity to neighboring structures, thus reducing the overallsize of the product incorporating the circuit panel.

It has also been proposed to package plural chips in a “stacked”arrangement, i.e., an arrangement where plural chips are placed one ontop of another. In a stacked arrangement, several chips can be mountedin an area of the circuit panel that is less than the total area of thechips. Certain stacked chip arrangements are disclosed, for example, incertain embodiments of the aforementioned U.S. Pat. Nos. 5,148,265,5,679,977, and U.S. Pat. No. 5,347,159, the disclosure of which isincorporated herein by reference. U.S. Pat. No. 4,941,033, alsoincorporated herein by reference, discloses an arrangement in whichchips are stacked on top of another and interconnected with one anotherby conductors on so-called “wiring films” associated with the chips.

Conventional chip contacts may have reliability challenges because of anon-optimal stress distribution at the contact and a mismatch of thecoefficient of thermal expansion (CTE) between a semiconductor chip, forexample, and the structure to which the chip is bonded. For example,when conductive contacts at a surface of a semiconductor chip areinsulated by a relatively thin and stiff dielectric material,significant stresses may be present at the contacts. In addition, whenthe semiconductor chip is bonded to conductive elements of a polymericsubstrate, the electrical connections between the chip and the higherCTE structure of the substrate will be under stress due to CTE mismatch.

Size is a significant consideration in any physical arrangement ofchips. The demand for more compact physical arrangements of chips hasbecome even more intense with the rapid progress of portable electronicdevices. Merely by way of example, devices commonly referred to as“smart phones” integrate the functions of a cellular telephone withpowerful data processors, memory and ancillary devices such as globalpositioning system receivers, electronic cameras, and local area networkconnections along with high-resolution displays and associated imageprocessing chips. Such devices can provide capabilities such as fullinternet connectivity, entertainment including full-resolution video,navigation, electronic banking and more, all in a pocket-size device.Complex portable devices require packing numerous chips into a smallspace. Moreover, some of the chips have many input and outputconnections, commonly referred to as “I/O's.” These I/O's must beinterconnected with the I/O's of other chips. The interconnectionsshould be short and should have low impedance to minimize signalpropagation delays. The components which form the interconnectionsshould not greatly increase the size of the assembly. Similar needsarise in other applications as, for example, in data servers such asthose used in internet search engines. For example, structures whichprovide numerous short, low-impedance interconnects between complexchips can increase the bandwidth of the search engine and reduce itspower consumption.

Despite the advances that have been made in semiconductor contactformation and interconnection, there is still a need for improvements inorder to minimize the size of semiconductor chips, while enhancingelectrical interconnection reliability. These attributes of the presentinvention are achieved by the construction of the microelectronicpackages as described hereinafter.

BRIEF SUMMARY OF THE INVENTION

In accordance with an aspect of the invention, a microelectronicassembly can include a substrate and an electrically conductive element.The substrate can have a CTE less than 10 ppm/° C., a major surfacehaving a recess not extending through the substrate, and a materialhaving a modulus of elasticity less than 10 GPa disposed within therecess. The electrically conductive element can include a joiningportion overlying the recess and extending from an anchor portionsupported by the substrate. The joining portion can be at leastpartially exposed at the major surface for connection to a componentexternal to the microelectronic unit.

In one embodiment, the substrate can have a CTE less than 7 ppm/° C. Ina particular embodiment, the joining portion can be movable so as toreduce stresses on the joining portion, such as may be present duringoperation, manufacturing, or testing of the microelectronic unit. In anexemplary embodiment, the substrate can consist essentially of onematerial selected from the group consisting of: semiconductor, glass,and ceramic. In one embodiment, the substrate can include a plurality ofactive semiconductor devices and the conductive element can beelectrically connected with at least one of the plurality of activesemiconductor devices. In a particular embodiment, the material disposedwithin the recess can include at least one material selected from thegroup consisting of: polyimide, silicone, and epoxy.

In an exemplary embodiment, the recess may not extend through thesubstrate. In one embodiment, the joining portion can extend in adirection substantially parallel to the major surface of the substrate.In a particular embodiment, the anchor portion and the joining portioncan extend in the same direction. In an exemplary embodiment, theconductive element can be electrically coupled with a conductive viaextending towards a second surface of the substrate opposite the majorsurface. In one embodiment, the conductive via can be exposed at thesecond surface. In a particular embodiment, the conductive via canextend within a hole in the substrate extending from the second surfaceto the major surface.

In one embodiment, the hole can include a first opening extending fromthe major surface towards the second surface and a second openingextending from the first opening to the second surface. Inner surfacesof the first and second openings can extend in first and seconddirections relative to the major surface, respectively, to define asubstantial angle. In an exemplary embodiment, a stacked assembly caninclude at least first and second microelectronic units, the secondmicroelectronic unit being stacked with the first microelectronic unit,with the substrate of the first microelectronic unit therein beingelectrically connected with a substrate of the second microelectronicunit. In a particular embodiment, the stacked assembly can furtherinclude a conductive mass electrically coupled to the joining portion ofthe first microelectronic unit and a conductive element of the secondmicroelectronic unit.

In accordance with another aspect of the invention, a microelectronicassembly can include a substrate and an electrically conductive element.The substrate can have a CTE less than 10 ppm/° C., a major surfacehaving a recess not extending through the substrate, and a materialhaving a modulus of elasticity less than 10 GPa disposed within therecess. The electrically conductive element can have an anchor portionfixed relative to the substrate, a joining portion at least partiallyoverlying the recess, and a connecting portion extending downwardly fromthe joining portion to the anchor portion. The joining portion canextend in a direction away from the anchor portion and can be exposed atthe major surface for connection to a component external to themicroelectronic unit. The connecting portion can have a contour notconforming to a contour of an inner surface of the recess.

In an exemplary embodiment, the substrate can have a CTE less than 7ppm/° C. In one embodiment, the joining portion can be movable so as toreduce stresses on the joining portion, such as may be present duringoperation, manufacturing, or testing of the microelectronic unit. In aparticular embodiment, the substrate can consist essentially of onematerial selected from the group consisting of: semiconductor, glass,and ceramic. In one embodiment, the substrate can include a plurality ofactive semiconductor devices and the conductive element can beelectrically connected with at least one of the plurality of activesemiconductor devices. In an exemplary embodiment, the connectingportion can extend into the recess.

In a particular embodiment, the conductive element can be electricallycoupled with a conductive via extending towards a second surface of thesubstrate opposite the major surface. In one embodiment, the conductivevia can be exposed at the second surface. In an exemplary embodiment,the conductive via can extend within a hole in the substrate extendingfrom the second surface to the major surface. In a particularembodiment, the hole can include a first opening extending from themajor surface towards the second surface and a second opening extendingfrom the first opening to the second surface. Inner surfaces of thefirst and second openings can extend in first and second directionsrelative to the major surface, respectively, to define a substantialangle. In one embodiment, the anchor portion can have a contourconforming to a contour of an inner surface of the hole. In an exemplaryembodiment, the joining portion can define an internal aperture.

In one embodiment, the aperture can extend through the joining portioninto the connecting portion. In a particular embodiment, at least aportion of the aperture can be filled with a dielectric material. In anexemplary embodiment, a stacked assembly can include at least first andsecond microelectronic units, the second microelectronic unit beingstacked with the first microelectronic unit, with the substrate of thefirst microelectronic unit therein being electrically connected with asubstrate of the second microelectronic unit. In a particularembodiment, the stacked assembly can further include a conductive masselectrically coupled to the joining portion of the first microelectronicunit and a conductive element of the second microelectronic unit.

In accordance with yet another aspect of the invention, a method offabricating a microelectronic unit can include the steps of forming anelectrically conductive element supported on a major surface of asubstrate having a CTE less than 10 ppm/° C., removing materialsupporting at least a joining portion of the conductive element from themajor surface to form a recess not extending through the substrate, anddepositing a material within the recess having a modulus of elasticityless than 10 GPa. The joining portion may not be supported by thesubstrate while an anchor portion of the conductive element adjacent thejoining portion may be supported by the substrate. The joining portioncan be at least partially exposed at the major surface of the substratefor connection to a component external to the microelectronic unit.

In one embodiment, the substrate can have a CTE less than 7 ppm/° C. Inan exemplary embodiment, the substrate can consist essentially of onematerial selected from the group consisting of: semiconductor, glass,and ceramic. In a particular embodiment, the substrate can include aplurality of active semiconductor devices, and the step of forming theconductive element can electrically connect the conductive element withat least one of the plurality of active semiconductor devices. In anexemplary embodiment, the step of forming the conductive element can beperformed such that the joining portion is disposed substantiallyparallel to the major surface. In one embodiment, the method can furtherinclude the steps of removing material from the substrate to form a holeextending from the major surface to a second surface of the substrateopposite the major surface, and forming a conductive via extendingwithin the hole such that the conductive via is electrically coupledwith the conductive element and extends towards the second surface.

In a particular embodiment, the step of removing material from thesubstrate to form a hole can include forming a first opening extendingfrom the major surface towards the second surface and a second openingextending from the first opening to the second surface. The innersurfaces of the first and second openings can extend in first and seconddirections relative to the major surface, respectively, to define asubstantial angle. In one embodiment, a method of fabricating a stackedassembly including at least first and second microelectronic units canfurther include the step of electrically connecting the substrate of thefirst microelectronic unit to a substrate of the second microelectronicunit.

In accordance with still another aspect of the invention, a method offabricating a microelectronic unit can include the steps of removingmaterial from a substrate having a CTE less than 10 ppm/° C. to form ahole extending from a major surface of the substrate to a second surfaceopposite the major surface, forming an electrically conductive elementhaving a joining portion extending above and supported on the majorsurface, an anchor portion fixed relative to the substrate, and aconnecting portion extending downwardly from the joining portion to theanchor portion, removing material supporting at least a joining portionof the conductive element from the major surface to form a recess suchthat the joining portion at least partially overlies the recess, anddepositing a material within the recess having a modulus of elasticityless than 10 GPa. A surface of the connecting portion can have a contourconforming to a contour of an inner surface of the hole. The contour ofthe surface of the connecting portion may not conform to a contour of aninner surface of the recess. The joining portion can be at leastpartially exposed at the major surface of the substrate for connectionto a component external to the microelectronic unit.

In a particular embodiment, the substrate can have a CTE less than 7ppm/° C. In an exemplary embodiment, the method of fabricating amicroelectronic unit can further include, before the step of forming theconductive element, forming a conductive via extending within the holeand extending towards the second surface, such that the step of formingthe conductive element electrically couples the conductive element withthe conductive via. In one embodiment, the step of forming theconductive element can be performed such that the joining portion isnon-centered relative to the connecting portion. In a particularembodiment, the substrate can consist essentially of one materialselected from the group consisting of: semiconductor, glass, andceramic. In an exemplary embodiment, the substrate can includes aplurality of active semiconductor devices, and the step of forming theconductive element can electrically connect the conductive element withat least one of the plurality of active semiconductor devices. In oneembodiment, the step of forming the conductive element can be performedsuch that the joining portion defines an internal aperture. In aparticular embodiment, the step of forming the conductive element can beperformed such that the aperture extends through the joining portioninto the connecting portion.

In one embodiment, the method of fabricating a microelectronic unit canfurther include the step of depositing a dielectric material into atleast a portion of the aperture. In a particular embodiment, the step ofremoving material from the substrate to form a hole can include forminga first opening extending from the major surface towards the secondsurface and a second opening extending from the first opening to thesecond surface. The inner surfaces of the first and second openings canextend in first and second directions relative to the major surface,respectively, to define a substantial angle. In an exemplary embodiment,a method of fabricating a stacked assembly including at least first andsecond microelectronic units can further include the step ofelectrically connecting the substrate of the first microelectronic unitto a substrate of the second microelectronic unit.

Further aspects of the invention provide systems which incorporatemicroelectronic structures according to the foregoing aspects of theinvention, composite chips according to the foregoing aspects of theinvention, or both in conjunction with other electronic devices. Forexample, the system may be disposed in a single housing, which may be aportable housing. Systems according to preferred embodiments in thisaspect of the invention may be more compact than comparable conventionalsystems.

Further aspects of the invention provide modules that can include aplurality of microelectronic assemblies according to the foregoingaspects of the invention. Each module can have a common electricalinterface for transport of signals to and from each of saidmicroelectronic assemblies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side sectional view illustrating a stacked assembly havinga contact structure in accordance with an embodiment of the invention.

FIG. 1B is one embodiment of a corresponding bottom-up sectional view ofthe stacked assembly of FIG. 3A taken along the line A-A.

FIG. 1C is another embodiment of a corresponding bottom-up sectionalview of the stacked assembly of FIG. 3A taken along the line A-A.

FIG. 1D is yet another embodiment of a corresponding bottom-up sectionalview of the stacked assembly of FIG. 3A taken along the line A-A.

FIGS. 2A-2D are sectional views illustrating stages of fabrication inaccordance with the embodiment of the invention depicted in FIG. 1A.

FIG. 3A is a side sectional view illustrating a stacked assembly havinga contact structure in accordance with an embodiment of the invention.

FIG. 3B is one embodiment of a corresponding bottom-up sectional view ofthe stacked assembly of FIG. 1A taken along the line B-B.

FIG. 3C is another embodiment of a corresponding bottom-up sectionalview of the stacked assembly of FIG. 1A taken along the line B-B.

FIG. 3D is yet another embodiment of a corresponding bottom-up sectionalview of the stacked assembly of FIG. 1A taken along the line B-B.

FIGS. 4A-4E are sectional views illustrating stages of fabrication inaccordance with the embodiment of the invention depicted in FIG. 3A.

FIG. 5 is a top perspective view of a substrate having a padelectrically connected with a chip in accordance with the presentinvention.

FIG. 6 is a side sectional view illustrating a substrate having acontact structure in accordance with another embodiment of theinvention.

FIG. 7 is a schematic depiction of a module according to one embodimentof the invention; and

FIG. 8 is a schematic depiction of a system according to one embodimentof the invention.

DETAILED DESCRIPTION

With reference to FIG. 1A, a stacked microelectronic assembly 10according to an embodiment of the present invention includes a firstmicroelectronic unit 12 and a second microelectronic unit 14. In someembodiments, the first and second microelectronic units 12 and 14 may bea semiconductor chip, a wafer, a dielectric substrate, or the like. Forexample, one or both of the first microelectronic unit 12 and the secondmicroelectronic unit 14 can include a memory storage element. As usedherein, a “memory storage element” refers to a multiplicity of memorycells arranged in an array, together with circuitry usable to store andretrieve data therefrom, such as for transport of the data over anelectrical interface.

The first microelectronic unit 12 includes a substrate 20 having arecess 30 extending from a major surface 21 partially through thesubstrate towards a second surface 22 opposite the major surface, and aconductive element 40 having an anchor portion 41 supported by thesubstrate, a joining portion 42 extending from the anchor portion, thejoining portion at least partially overlying the recess 30 and at leastpartially exposed at the major surface for interconnection with acomponent external to the first microelectronic unit, and an end portion46. As shown, the end portion 46 is located at an end of the joiningportion 42. A dielectric region 50 overlies an inner surface 31 at leastwithin the recess 30.

In FIG. 1A, the directions parallel to the major surface 21 are referredto herein as “horizontal” or “lateral” directions, whereas thedirections perpendicular to the front surface are referred to herein asupward or downward directions and are also referred to herein as the“vertical” directions. The directions referred to herein are in theframe of reference of the structures referred to. Thus, these directionsmay lie at any orientation to the normal or gravitational frame ofreference. A statement that one feature is disposed at a greater height“above a surface” than another feature means that the one feature is ata greater distance in the same orthogonal direction away from thesurface than the other feature. Conversely, a statement that one featureis disposed at a lesser height “above a surface” than another featuremeans that the one feature is at a smaller distance in the sameorthogonal direction away from the surface than the other feature.

The substrate 20 preferably has a coefficient of thermal expansion(“CTE”) less than 10*10⁻⁶/° C. (or ppm/° C.). In a particularembodiment, the substrate 20 can have a coefficient of thermal expansion(“CTE”) less than 7*10⁻⁶/° C. (or ppm/° C.). The substrate 20 preferablyconsists essentially of a material such as semiconductor, glass, orceramic. In embodiments wherein the substrate 20 is made of asemiconductor, such as silicon, a plurality of active semiconductordevices (e.g., transistors, diodes, etc.) can be disposed in an activesemiconductor region thereof located at and/or below the major surface21 or the second surface 22. The thickness of the substrate 20 betweenthe major surface 21 and the second surface 22 typically is less than200 μm, and can be significantly smaller, for example, 130 μm, 70 μm oreven smaller.

The substrate 20 can further include a dielectric layer disposed betweenthe major surface 21 and at least one conductive element 40. Adielectric layer can overlie the second surface 22. Such a dielectriclayer can electrically insulate conductive elements from the substrate20. One or both of these dielectric layers can be referred to as a“passivation layer” of the first microelectronic unit 12. The dielectriclayer can include an inorganic or organic dielectric material or both.The dielectric layer may include an electrodeposited conformal coatingor other dielectric material, for example, a photoimageable polymericmaterial, for example, a solder mask material.

The microelectronic element 12 can include one or more conductiveelements 40 exposed at the major surface 21 of the substrate 20. Thejoining portion 42 of each conductive element 40 can be exposed at themajor surface 21 for interconnection with a component external to thefirst microelectronic element 12, such as the second microelectronicelement 14. While not specifically shown in the figures, activesemiconductor devices in the substrate 20 can be conductively connectedto the joining portions 42. The active semiconductor devices, thus, canbe accessible conductively through wiring incorporated extending withinor above one or more dielectric layers of the substrate 20. Theconductive elements 40 (and any of the other conductive elementsdescribed herein) can be made from any electrically conductive metal,including for example, copper or gold.

As shown, for example, in FIG. 1C, the joining portion 42′ can have thebottom-view shape of a conductive bond pad, e.g., a thin flat member.Each joining portion 42 can have any bottom-view shape, including forexample, a rectangular trace shape, as shown in FIG. 1B, a circular padshape, as shown in FIG. 1C, an oval shape, a square shape, a triangularshape, or a more complex shape. In other embodiments, the joiningportion 42 can be any other type of conductive contact, including forexample, a conductive post.

The joining portion 42 can be aligned with the recess 30 and can bedisposed wholly or partly within an area of the substrate 20 defined bythe recess. As seen in FIG. 1A, the joining portion 42 is whollydisposed within an area defined by the recess 30. As shown, a planedefined by a top surface 43 of the joining portion 42 is substantiallyparallel to a plane defined by the major surface 21 of the substrate 20.As shown, a bottom surface 44 of the joining portion 42 is located at aplane defined by the major surface of the substrate 20. In otherembodiments, the bottom surface 44 of the joining portion 42 can belocated above or below the plane defined by the major surface 21. Theend portion 46 of the conductive element 40 is not supported by thesubstrate 20, such that the end portion can be cantilevered with respectto the anchor portion 41. Such an unsupported end portion 46 of thejoining portion 42 that overlies the major surface 21 and is locatedadjacent to the dielectric region 50 can be free to move relative to thesupported anchor portion 41, such that the joining portion 42 canfunction as a cantilever.

As used in this disclosure, a statement that an electrically conductiveelement is “exposed at” a surface of a substrate or a dielectric elementoverlying a surface of the substrate indicates that the electricallyconductive element is available for contact with a theoretical pointmoving in a direction perpendicular to the surface of the dielectricelement toward the surface of the dielectric element from outside thedielectric element. Thus, a terminal or other conductive element whichis exposed at a surface of a dielectric element may project from suchsurface; may be flush with such surface; or may be recessed relative tosuch surface and exposed through a hole or depression in the dielectric.

While essentially any technique usable for forming conductive elementscan be used to form the conductive elements described herein, particulartechniques as discussed in greater detail in the commonly owned U.S.patent application Ser. No. 12/842,669, filed Jul. 23, 2010, can beemployed, which is hereby incorporated by reference herein. Suchtechniques can include, for example, selectively treating a surface witha laser or with mechanical processes such as milling or sandblasting soas to treat those portions of the surface along the path where theconductive element is to be formed differently than other portions ofthe surface. For example, a laser or mechanical process may be used toablate or remove a material such as a sacrificial layer from the surfaceonly along a particular path and thus form a groove extending along thepath. A material such as a catalyst can then be deposited in the groove,and one or more metallic layers can be deposited in the groove.

The end portion 46 of the conductive element 40 is shown in the figuresas not extending laterally (i.e., in a direction parallel to the majorsurface 21 of the substrate 20) beyond an outer boundary 32 (FIG. 1B) ofthe recess 30. In any of the embodiments disclosed herein, the endportion of the conductive element and/or the joining portion can extendlaterally beyond the outer boundary of the recess. In one embodiment, anend of the joining portion can be coupled to a conductive trace (notshown) that extends laterally beyond the outer boundary of thecorresponding recess, but the joining portion can still be movablerelative to the corresponding substrate in the manner described below.

The recess 30 extends from the major surface 21 partially through thesubstrate 20 towards the second surface 22. The inner surface 31 of therecess 30 can extend from the major surface 21 through the substrate 20at any angle. Preferably, the inner surface 31 extends from the majorsurface 21 at an angle between 0 and 90 degrees to the horizontal planedefined by the major surface 21. The inner surface 31 can have aconstant slope or a varying slope. For example, the angle or slope ofthe inner surface 31 relative to the horizontal plane defined by themajor surface 21 can decrease in magnitude (i.e., become less positiveor less negative) as the inner surface 31 penetrates further towards thesecond surface 22.

The recess 30 can have any bottom-view shape, including for example, anoval, as shown in FIG. 1B, or a circle, as shown in FIG. 1C. In theembodiment shown in FIG. 1B, recess 30 has a width W in a first lateraldirection along the major surface 21, and the recess has a length L in asecond lateral direction along the major surface transverse to the firstlateral direction, the length being greater than the width. In someexamples, the recess 30 can have any three-dimensional shape, includingfor example, a cylinder, a cube, a prism, or a frustoconical shape,among others.

In a particular embodiment, the recess 30 can be a rectangular channelwith a plurality of joining portions 42 at least partially overlying therecess, as shown in FIG. 1D. Any number of joining portions 42 canoverlie a single recess 30, and the joining portions can be arranged inany geometric configuration overlying a single recess. For example,three joining portions 42 can be arranged along a common axis overlyinga single recess 30, as shown in FIG. 1D.

In the embodiments shown, the dielectric region 50 fills the recess 30such that a contour of the dielectric region conforms to a contour ofthe recess (i.e., the shape of the inner surface 31 of the recess). Thedielectric region 50 can provide good dielectric isolation with respectto the substrate 20. The dielectric region 50 can be compliant, having asufficiently low modulus of elasticity and sufficient thickness suchthat the product of the modulus and the thickness provide compliancy.Preferably, the joining portion 42 of the conductive element 40 at leastpartially overlies the dielectric region 50. A compliant dielectricregion 50 can allow the joining portion 42 of the conductive element 40to flex or move somewhat relative to the substrate 20 and the anchorportion 41 of the conductive element supported thereon when an externalload is applied to the joining portion. In that way, the bond betweenthe joining portions 42 of the first microelectronic unit 12 andterminals of the second microelectronic unit 14 may be able to betterwithstand thermal strain due to mismatch of the coefficient of thermalexpansion (“CTE”) between the first and second microelectronic units.

As used herein in connection with a joining portion of a conductiveelement, “movable” shall mean that the joining portion is capable ofbeing displaced relative to the major surface of the substrate by anexternal load applied thereto, to the extent that the displacementappreciably relieves or reduces mechanical stresses, such as thosecaused by differential thermal expansion during operation,manufacturing, or testing of the microelectronic unit which would bepresent in the electrical connection with the conductive element absentsuch displacement.

The degree of compliancy provided by the product of the thickness of thedielectric region 50 and its modulus of elasticity can be sufficient tocompensate for strain applied to the joining portions 42 due to thermalexpansion mismatch between the first microelectronic unit 12 and thesecond microelectronic unit 14 to which the first microelectronic unitis mounted through the joining portions. An underfill (not shown) can beprovided between an outer surface 51 of the dielectric region 50 andsuch second microelectronic unit 14 to enhance resistance to thermalstrain due to CTE mismatch.

In the embodiments shown, the outer surface 51 (FIG. 1A) of thedielectric region 50 is located within a plane defined by the majorsurface 21 of the substrate 20. Alternatively, the outer surface 51 ofthe dielectric region 50 can extend above a plane defined by the majorsurface 21 of the substrate 20, or the outer surface of the dielectricregion can be recessed below a plane defined by the major surface of thesubstrate.

A dielectric layer 25 can overlie the major surface 21 of the substrate20 and portions of the conductive elements that are not the joiningportions 42, to provide good dielectric isolation with respect to thesubstrate and the portions of the conductive elements that are not thejoining portions. The dielectric layer 25 can include an inorganic ororganic dielectric material or both. In a particular embodiment, thedielectric layer 25 can include the same compliant dielectric materialas the dielectric region 50. In an exemplary embodiment, the dielectriclayer 25 can be formed continuously with the dielectric region 50.

The second microelectronic unit 14 can include a substrate 15 andconductive contacts 16 a and 16 b at least partially exposed at a majorsurface 17 of the substrate for interconnection with joining portions 42of the first microelectronic unit 12. By providing joining portions 42in the first microelectronic unit 12 and rear conductive contacts in thesecond microelectronic unit 14, a plurality of microelectronic units canbe stacked one on top of the other to form the stacked microelectronicassembly 10. In such arrangement, the joining portions 42 are alignedwith the conductive contacts 16 a and 16 b.

As shown in FIG. 1A, the conductive contact 16 a is a conductive post.The conductive post 16 a can be any type of conductive post and may haveany shape, including a frustoconical shape. The base and tip of eachconductive post 16 a may be substantially circular or have a differentshape, e.g., oblong. Other examples of conductive posts can be used, asshown and described in the commonly-owned U.S. patent application Ser.No. 12/832,376, filed on Jul. 8, 2010. The conductive contact 16 b isshown as a conductive pad. The conductive pad 16 b can have any shape,including circular, square, oblong, rectangular, or a more complexshape.

Connection between the first microelectronic unit 12 and the secondmicroelectronic unit 14 can be through conductive masses 18. Thedielectric layer 25 and the dielectric region 50 at the major surface 21of the substrate and a dielectric layer (e.g., a passivation layer)overlying the major surface 17 of the substrate 15 can provideelectrical isolation between the first microelectronic unit 12 and thesecond microelectronic unit 14 except where interconnection is provided.

The conductive masses 18 can comprise a fusible metal having arelatively low melting temperature, e.g., solder, tin, or a eutecticmixture including a plurality of metals. Alternatively, the conductivemasses 18 can include a wettable metal, e.g., copper or other noblemetal or non-noble metal having a melting temperature higher than thatof solder or another fusible metal. Such wettable metal can be joinedwith a corresponding feature, e.g., a fusible metal feature of aninterconnect element such as the second microelectronic unit 14 toexternally interconnect the first microelectronic unit 12 to suchinterconnect element. In a particular embodiment, the conductive masses18 can include a conductive material interspersed in a medium, e.g., aconductive paste, e.g., metal-filled paste, solder-filled paste orisotropic conductive adhesive or anisotropic conductive adhesive.

A method of fabricating the microelectronic assembly 10 (FIGS. 1A-1D)will now be described, with reference to FIGS. 2A-2D. As illustrated inFIG. 2A, the first microelectronic unit 12 includes the substrate 20 andone or more conductive elements 40 overlying the major surface 21. Theconductive elements 40 may be insulated from the substrate 20 by adielectric layer such as a passivation layer (not shown).

In the stage of fabrication illustrated in FIG. 2B, a dielectric layer25 is formed on the major surface 21 of the substrate 20 and serves asan etch mask layer where it is desired to preserve remaining portions ofthe major surface. For example, the dielectric layer 25 can be aphotoimageable layer, e.g., a photoresist layer, that is deposited andpatterned to cover only portions of the major surface 21, after which atimed etch process can be conducted to form the recess 30. The joiningportion 42 of each conductive element 40 can remain at least partiallyexposed at the major surface (i.e., not covered by the dielectric layer25) for connection to a component external to the first microelectronicunit 12.

Various methods can be used to form the dielectric layer 25. In oneexample, a flowable dielectric material is applied to the major surface21 of the substrate 20, and the flowable material is then more evenlydistributed across the major surface during a “spin-coating” operation,followed by a drying cycle which may include heating. In anotherexample, a thermoplastic film of dielectric material can be applied tothe major surface 21 after which the assembly is heated, or is heated ina vacuum environment, i.e., placed in an environment under lower thanambient pressure. In another example, vapor deposition can be used toform the dielectric layer 25.

In still another example, the assembly including the substrate 20 can beimmersed in a dielectric deposition bath to form a conformal dielectriccoating or dielectric layer 25. As used herein, a “conformal coating” isa coating of a particular material that conforms to a contour of thesurface being coated, such as when the dielectric layer 25 conforms to acontour of the major surface 21. An electrochemical deposition methodcan be used to form the conformal dielectric layer 25, including forexample, electrophoretic deposition or electrolytic deposition.

In one example, an electrophoretic deposition technique can be used toform the conformal dielectric coating, such that the conformaldielectric coating is only deposited onto exposed conductive andsemiconductive surfaces of the assembly. During deposition, thesemiconductor device wafer is held at a desired electric potential andan electrode is immersed into the bath to hold the bath at a differentdesired potential. The assembly is then held in the bath underappropriate conditions for a sufficient time to form an electrodepositedconformal dielectric layer 25 on exposed surfaces of the substrate whichare conductive or semiconductive, including but not limited to along themajor surface 21. Electrophoretic deposition occurs so long as asufficiently strong electric field is maintained between the surface tobe coated thereby and the bath. As the electrophoretically depositedcoating is self-limiting in that after it reaches a certain thicknessgoverned by parameters, e.g., voltage, concentration, etc. of itsdeposition, deposition stops.

Electrophoretic deposition forms a continuous and uniformly thickconformal coating on conductive and/or semiconductive exterior surfacesof the assembly. In addition, the electrophoretic coating can bedeposited so that it does not form on a remaining passivation layeroverlying the major surface 21, due to its dielectric (nonconductive)property. Stated another way, a property of electrophoretic depositionis that is does not form on a layer of dielectric material overlying aconductor provided that the layer of dielectric material has sufficientthickness, given its dielectric properties. Typically, electrophoreticdeposition will not occur on dielectric layers having thicknessesgreater than about 10 microns to a few tens of microns. The conformaldielectric layer 25 can be formed from a cathodic epoxy depositionprecursor. Alternatively, a polyurethane or acrylic deposition precursorcould be used. A variety of electrophoretic coating precursorcompositions and sources of supply are listed in Table 1 below.

TABLE 1 ECOAT NAME POWERCRON 645 POWERCRON 648 CATHOGUARD 325MANUFACTURERS MFG PPG PPG BASF TYPE CATHODIC CATHODIC CATHODIC POLYMERBASE EPOXY EPOXY EPOXY LOCATION Pittsburgh, PA Pittsburgh, PASouthfield, MI APPLICATION DATA Pb/Pf-free Pb-free Pb or Pf-free Pb-freeHAPs, g/L 60-84 COMPLIANT VOC, g/L (MINUS WATER) 60-84 <95 CURE 20min/175 C. 20 min/175 C. FILM PROPERTIES COLOR Black Black BlackTHICKNESS, μm 10-35 10-38 13-36 PENCIL HARDNESS 2H+ 4H BATHCHARACTERISTICS SOLIDS, % wt. 20 (18-22)  20 (19-21)  17.0-21.0 pH (25C.) 5.9 (5.8-6.2) 5.8 (5.6-5.9) 5.4-6.0 CONDUCTIVITY (25 C.) μS1000-1500 1200-1500 1000-1700 P/B RATIO 0.12-0.14 0.12-0.16 0.15-0.20OPERATION TEMP., C. 30-34 34 29-35 TIME, sec 120-180  60-180  120+ ANODESS316 SS316 SS316 VOLTS 200-400 >100  ECOAT NAME ELECTROLAC LECTRASEALDV494 LECTROBASE 101 MANUFACTURERS MFG MACDERMID LVH COATINGS LVHCOATINGS TYPE CATHODIC ANODIC CATHODIC POLYMER BASE POLYURETHANEURETHANE URETHANE LOCATION Waterbury, CT Birmingham, UK Birmingham, UKAPPLICATION DATA Pb/Pf-free Pb-free Pb-free HAPs, g/L VOC, g/L (MINUSWATER) CURE 20 min/149 C. 20 min/175 C. 20 min/175 C. FILM PROPERTIESCOLOR Clear (+dyed) Black Black THICKNESS, μm 10-35 10-35 PENCILHARDNESS 4H BATH CHARACTERISTICS SOLIDS, % wt. 7.0 (6.5-8.0) 10-12  9-11pH (25 C.) 5.5-5.9 7-9 4.3 CONDUCTIVITY (25 C.) μS 450-600 500-800400-800 P/B RATIO OPERATION TEMP., C. 27-32 23-28 23-28 TIME, sec 60-120 ANODE SS316 316SS 316SS VOLTS 40, max  50-150

In another example, the dielectric layer can be formed electrolytically.This process is similar to electrophoretic deposition, except that thethickness of the deposited layer is not limited by proximity to theconductive or semiconductive surface from which it is formed. In thisway, an electrolytically deposited dielectric layer can be formed to athickness that is selected based on requirements, and processing time isa factor in the thickness achieved.

Thereafter, in the stage of fabrication illustrated in FIG. 2C, therecess 30 can be formed extending downwardly from the major surface 21towards the second surface 22 of the substrate 20. The recess 30 can beformed for example, by selectively etching the substrate 20 to removematerial of the substrate, after forming a mask layer (e.g., thedielectric layer 25) where it is desired to preserve remaining portionsof the major surface 21. The recess 30 can be formed such that materialof the substrate 20 supporting at least the joining portion 42 isremoved.

The inner surfaces 31 of the recess 30, extending downwardly from themajor surface 21 towards the second surface 22, may be sloped, i.e., mayextend at angles other a normal angle (right angle) to the majorsurface, as shown in FIG. 2C. Wet etching processes, e.g., isotropicetching processes and sawing using a tapered blade, among others, can beused to form recesses 30 having sloped inner surfaces 31. Laserablation, mechanical milling, chemical etching, plasma etching,directing a jet of fine abrasive particles towards the substrate 20,among others, can also be used to form the recesses 30 (or any otherhole or opening described herein) having sloped inner surfaces 31.

Alternatively, instead of being sloped, the inner surfaces of the recess30 may extend in a vertical or substantially vertical directiondownwardly from the major surface 21 substantially at right angles tothe major surface. Anisotropic etching processes, laser ablation,mechanical removal processes, e.g., milling, ultrasonic machining,directing a jet of fine abrasive particles towards the substrate 20,among others, can be used to form recesses 30 having essentiallyvertical inner surfaces.

Thereafter, in the stage of fabrication illustrated in FIG. 2D, thedielectric region 50 is formed inside the recess 30. The dielectricregion 50 can include an inorganic material, a polymeric material, orboth. Optionally, the dielectric region 50 can be formed such that theexposed outer surface 51 of the region is co-planar or substantiallyco-planar with the major surface 21 of the substrate 20 or an exposedsurface of the dielectric layer 25. For example, a self-planarizingdielectric material can be deposited in the recess 30, e.g., by adispensing or stenciling process. In another example, a grinding,lapping, or polishing process can be applied to the major surface 21 ofthe substrate 20 or the exposed surface of the dielectric layer 25 afterforming the dielectric region 50 to planarize the surface of thedielectric region 50 to the major surface 21 or the exposed surface ofthe dielectric layer 25.

Thereafter, referring again to FIG. 1A, the first microelectronic unit12 can be stacked on top of the second microelectronic unit 14, therebyforming the stacked microelectronic assembly 10. As described above,connection between the first microelectronic unit 12 and the secondmicroelectronic unit 14 can be through conductive masses 18. Theconductive masses 18 can provide an electrical connection between thejoining portions 42 of the first microelectronic unit 12 and theconductive contacts 16 a and 16 b of the second microelectronic unit 14.In such arrangement, the joining portions 42 are aligned with theconductive contacts 16 a and 16 b.

Referring now to FIG. 3A, a stacked microelectronic assembly 110according to another embodiment of the present invention includes afirst microelectronic unit 112 and a second microelectronic unit 114.The microelectronic units 112 and 114 can have similar functions as themicroelectronic units 12 and 14 described above.

The first microelectronic unit 112 includes a substrate 120 having arecess 130 a and 130 b extending from a major surface 121 partiallythrough the substrate towards a second surface 122 opposite the majorsurface, and conductive elements 140 a and 140 b each having arespective anchor portion 141 a or 141 b supported by the substrate, arespective joining portion 142 a or 142 b at least partially overlyingthe respective recess 130 a or 130 b and at least partially exposed atthe major surface for interconnection with a component external to thefirst microelectronic unit, one or more respective connecting portions145 a or 145 b extending between the anchor and joining portions, andend portions 146. As shown, the end portions 146 are located at an endof each joining portion 142 a and 142 b. A dielectric region 150overlies an inner surface 131 at least within the recess 130 a or 130 b.

The substrate 120 further includes a hole 160 extending from the opening130 to the second surface 122 and a conductive via 170 extending withinthe hole from the respective anchor portion 141 a or 141 b to the secondsurface. The conductive via 170 includes a contact portion 180 exposedat the second surface 122 for interconnection with a component externalto the stacked microelectronic assembly 110.

The substrate 120 has similar properties as the substrate 20 describedabove with reference to FIGS. 1A through 2D. For example, the substrate120 preferably has a CTE less than 10 ppm/° C., and the substrate 120preferably consists essentially of a material such as a semiconductor,glass or ceramic. In embodiments wherein the substrate 120 is made of asemiconductor, such as silicon, a plurality of active semiconductordevices can be disposed therein. The substrate 120 can further include adielectric layer (e.g., a “passivation layer”) overlying the majorsurface 121 and/or the second surface 122.

The microelectronic element 112 can include one or more conductiveelements 140 a and 140 b exposed at the major surface 121 of thesubstrate 120. The joining portions 142 a and 142 b of the respectiveconductive elements 140 a and 140 b can be exposed at the major surface121 for interconnection with a component external to the firstmicroelectronic element 112, such as the second microelectronic element114. Active semiconductor devices in the substrate 120 can beconductively connected to the joining portions 142 a and 142 b.

Each joining portion 142 a and 142 b can have any bottom-view shape. Asshown, for example, in FIG. 3B, the joining portions 142 a and 142 b canhave the shape of a conductive bond pad, e.g., a thin flat member, or aportion of a conductive bond pad. For example, the joining portion 142 bshown in FIGS. 3B and 3C has a round, solid bottom-view shape. Thejoining portion 142 a shown in FIG. 3B has a round bottom-view shapewith an aperture 147 extending therethrough. The joining portionsegments 142 a′ shown in FIG. 3C together have a round bottom-viewshape, with the aperture 147 extending therethrough and gaps 148extending between adjacent joining portion segments.

The joining portions 142 a and 142 b can have other bottom-view shapes,including, for example, a rectangular trace shape or rectangular traceshape portions. For example, the joining portion 142 b″ shown in FIG. 3Dhas a rectangular trace shape. The joining portions 142 a″ shown in FIG.3D are rectangular trace-shaped portions having the aperture 147 locatedtherebetween. The joining portions 142 a and 142 b can alternativelyhave more complex shapes. In other embodiments, the joining portions 142a and 142 b can be any other type of conductive contact, including forexample, a conductive post.

The joining portions 142 a and 142 b can be aligned with the respectiverecess 130 a or 130 b and can be disposed wholly or partly within anarea of the substrate 120 defined by the recess. As seen in FIG. 3A, thejoining portions 142 a and 142 b are wholly disposed within an areadefined by the respective recess 130 a or 130 b. As shown, a planedefined by top surfaces 143 a and 143 b of the respective joiningportions 142 a or 142 b are substantially parallel to a plane defined bythe major surface 121 of the substrate 120. As shown, bottom surfaces144 a and 144 b of the respective joining portions 142 a or 142 b arelocated at a plane defined by the major surface 121 of the substrate120. In other embodiments, the bottom surfaces 144 a and 144 b can belocated above or below the plane defined by the major surface 121.

The connecting portions 145 a and 145 b extend downwardly from therespective joining portions 142 a or 142 b to the respective anchorportion 141 a or 141 b. At least a portion of the connecting portions145 a and 145 b have a contour not conforming to a contour of the innersurfaces 131 of the respective recess 130 a or 130 b. In a particularembodiment, there can be a single trace-shaped connecting portion 145 bextending from the anchor portion 141 b to the joining portion 142 b. Inalternative embodiments, there can be any number of connecting portionsextending from the anchor portion. For example, in one embodiment, theconnecting portion 145 a can have a hollow frustoconical shape with aninternal aperture 147, such as in the embodiment shown in FIG. 3B. Inanother embodiment, there can be four individual connecting portionsextending between a single anchor portion 141 a and respective joiningportions such as the joining portions 142 a′ shown in FIG. 3C. In stillanother embodiment, there can be two individual connecting portionsextending between a single anchor portion 141 a and respective joiningportions such as the joining portions 142 a″ shown in FIG. 3D. Thejoining portions 142 a and 142 b preferably are non-centered relative tothe respective connecting portions 145 a or 145 b, such that the endportion 146 of the respective conductive element 140 a or 140 b can becantilevered with respect to the respective anchor portion 141 a or 141b.

The recesses 130 a and 130 b are similar to the recess 30 shown anddescribed above with reference to FIGS. 1A through 2D. The recesses 130a and 130 b extend from the major surface 121 partially through thesubstrate 120 towards the second surface 122. The inner surfaces 131 ofthe recesses 130 a and 130 b can extend from the major surface 121through the substrate 120 at any angle. Preferably, the inner surfaces131 extend from the major surface 121 at an angle between 0 and 90degrees to the horizontal plane defined by the major surface 121.

The recesses 130 a and 130 b can have any bottom-view shape, includingfor example, an oval, such as the recess 130 b shown in FIGS. 1B-1D, ora circle, such as the recess 130 a shown in FIGS. 1B and 1C. In someexamples, the recesses 130 a and 130 b can have any three-dimensionalshape, including for example, a cylinder, a cube, a prism, or afrustoconical shape, among others. In a particular embodiment, therecesses 130 a and 130 b can be a rectangular channel with a pluralityof respective joining portions 142 a and 142 b at least partiallyoverlying the recess, in a configuration similar to that of the joiningportions 42 shown in FIG. 1D.

The dielectric region 150 has similar possible configurations andproperties as the dielectric region 50 shown and described above withreference to FIGS. 1A through 2D. For example, in the embodiments shownin FIGS. 3A-3D, the dielectric region 150 fills the recesses 130 a and130 b such that a contour of the dielectric region conforms to a contourof the recess (i.e., the shape of the inner surfaces 131 of therecesses). The dielectric region 150 can be compliant, having asufficiently low modulus of elasticity and sufficient thickness suchthat the product of the modulus and the thickness provide compliancy.Preferably, the joining portions 142 a and 142 b at least partiallyoverlie the dielectric region 150, such that the joining portions can bemovable relative to the substrate 120.

Similar to the dielectric layer 25 described above with reference toFIGS. 1A through 2D, a dielectric layer 125 can overlie the majorsurface 121 of the substrate 120 and portions of the conductive elements140 a and 140 b that are not the joining portions 142 a and 142 b, toprovide good dielectric isolation with respect to the substrate and theportions of the conductive elements that are not the joining portions.

As shown in FIGS. 3A-3D, the hole 160 is staged, including a firstopening 161 extending from the opening 130 towards the second surface122 and a second opening 162 extending from the first opening to thesecond surface. The staged hole 160 can have any of the structures shownand described in greater detail in the commonly owned U.S. patentapplication Ser. No. 12/842,717, filed Jul. 23, 2010, and the commonlyowned U.S. Patent Application Publication No. 2008/0246136, which arehereby incorporated by reference herein. In other embodiments, such asthe hole 60 b shown and described with reference to FIG. 6, the hole canhave a more simple non staged structure.

The first opening 161 extends from the recess 130 partially through thesubstrate 120 towards the second surface 122. The first opening 161includes inner surfaces 163 that extend from the recess 130 through thesubstrate 120 at an angle between 0 and 90 degrees to the horizontalplane defined by the major surface 121. The inner surfaces 163 can havea constant slope or a varying slope. For example, the angle or slope ofthe inner surfaces 163 relative to the horizontal plane defined by themajor surface 121 can decrease in magnitude (i.e., become less positiveor less negative) as the inner surfaces 163 penetrate further towardsthe second surface 122. As shown, for example, in FIG. 4D, the firstopening 161 has a width W1 at the recess 130 and a width W2 where thefirst opening meets the second opening 162 that is less than W1 suchthat the first opening is tapered in a direction from the major surface121 towards the second surface 122. In other examples, the first openingcan have a constant width, or the first opening can be tapered in adirection from the second surface towards the front surface. The firstopening 161 can have any three-dimensional shape, including for example,cubic, cylindrical, frustoconical, or a prism, among others.

The second opening 162 extends from the first opening 161 partiallythrough the substrate 120 towards the second surface 122. The secondopening 162 includes inner surfaces 164 that extend from the firstopening 161 through the substrate 120 at an angle between 0 and 90degrees to the horizontal plane defined by the major surface 121.Similar to the inner surfaces 163 described above, the inner surfaces164 can have a constant slope or a varying slope. As shown, for example,in FIG. 4D, the second opening 162 has a width W3 where the secondopening meets the first opening 161 and a width W4 at the second surface122 that is greater than W3 such that the first opening is tapered in adirection from the second surface 122 towards the major surface 121. Inother examples, the second opening can have a constant width, or thesecond opening can be tapered in a direction from the front surfacetowards the second surface. The second opening 162 can have anythree-dimensional shape, including for example, cubic, cylindrical,frustoconical, or a prism, among others.

In a particular embodiment, the inner surfaces 163 and 164 can extend infirst and second directions relative to the major surface 121,respectively, to define a substantial angle. Any number of firstopenings 161 can extend from a single second opening 162, and any numberof second openings can extend from a single first opening. The first andsecond openings 161 and 162 can be arranged in any geometricconfiguration relative to each other and relative to the substrate 120.Particular examples of various first and second opening configurationsand methods of forming these configurations are described in theaforementioned commonly owned U.S. patent application Ser. No.12/842,717 and U.S. Patent Application Publication No. 2008/0246136.

The anchor portions 141 a and 141 b of the respective conductiveelements 140 a and 140 b preferably have contours that conform to acontour of the respective first opening 161, such that the anchorportions have positions that are fixed relative to the substrate 120. Ananchor portion 141 a or 141 b can serve as a fulcrum about which anattached joining portion 142 a or 142 b can pivot when put undermechanical stress such as that caused by differential thermal expansionrelative to an attached microelectronic unit.

The conductive via 170 extends through the hole 160 between therespective anchor portion 141 a or 141 b and the second surface 122. Asshown in FIG. 3A, the conductive via 170 can fill all of the volumewithin the second opening 162 inside of an optional dielectric layer(not shown) that can electrically insulate the substrate 120 from theconductive via. The conductive via 170 can conform to the contour of thesecond opening 162. The conductive via 170 may have a cylindrical orfrustoconical shape. The conductive via 170 can be made from a metal oran electrically conductive compound of a metal, including for example,copper or gold.

In other embodiments (not shown), a contour of the conductive via 170(i.e., the shape of the outer surface of the conductive via) does notconform to a contour of the second opening 162 (i.e., the shape of theinner surface 164 of the second opening). In such non-conformalconductive via embodiments, the conductive via 170 can have any shape,including for example, a cylindrical shape, frustoconical shape, or acombination of a cylindrical and a frusto-conical shape at differentdistances from the second surface 122.

The conductive via 170 can be solid or hollow. In some embodiments, theconductive via can include an internal space that is filled with adielectric material. For example, the conductive via 170 can be formedby depositing a metal overlying the inner surface 164 of the secondopening 162, thereby producing a conductive layer overlying the innersurface second opening. Particular examples of various conductive viaconfigurations and methods of forming these configurations are describedin the aforementioned commonly owned U.S. patent application Ser. No.12/842,717 and U.S. Patent Application Publication No. 2008/0246136.

The conductive vias 170 each include a contact portion 180 exposed atthe second surface 122 for interconnection with a component external tothe stacked microelectronic assembly 110. In some embodiments, eachconductive via 170 can be electrically coupled to a separate conductivecontact exposed at the second surface 122.

The second microelectronic unit 114 is similar to the secondmicroelectronic unit 14 shown and described above with reference to FIG.1A. The second microelectronic unit 114 can include a substrate 115 andconductive contacts 116 at least partially exposed at a major surface117 of the substrate for interconnection with the joining portions 142 aand 142 b of the first microelectronic unit 112.

As shown in FIG. 3A, the conductive contacts 116 are conductive pads.The conductive pads 116 can have any shape, including circular, square,oblong, rectangular, or a more complex shape. In particular embodiments,the conductive contacts 116 can be any type of conductive contact,including, for example, a conductive post such as the conductive post 16a shown in FIG. 1A. Other examples of conductive posts can be used, asshown and described in the commonly-owned U.S. patent application Ser.No. 12/832,376, filed on Jul. 8, 2010.

Connection between the first microelectronic unit 112 and the secondmicroelectronic unit 114 can be through conductive masses 118, in amanner similar to that described with reference to FIGS. 1A through 2D.The dielectric layer 125 and the dielectric region 150 at the majorsurface 121 of the substrate 120 and a dielectric layer (e.g., apassivation layer) overlying the major surface 117 of the substrate 115can provide electrical isolation between the first microelectronic unit112 and the second microelectronic unit 114 except where interconnectionis provided.

A method of fabricating the microelectronic assembly 110 (FIGS. 3A-3D)will now be described, with reference to FIGS. 4A-4D. In the stage offabrication illustrated in FIG. 4A, the first microelectronic unit 112includes the substrate 120. The holes 160 can be formed extending fromthe major surface 121 to the second surface 122 of the substrate 120 byremoving material from the substrate. In a particular embodiment, thefirst opening 161 can be formed extending inwardly from the majorsurface 121, and the second opening can be formed extending inwardlyfrom the second surface 122. In other embodiments, either or both of thefirst and second openings 161 and 162 can be formed from either themajor or second surfaces 121 and 122.

The holes 160 can be formed in a similar manner and using similarprocesses as described above with respect to forming the recess 30. Forexample, the holes 160 can be formed by selectively etching thesubstrate 120 to remove material of the substrate, after forming a masklayer where it is desired to preserve remaining portions of the majorsurface 121. Similar to the recess 30, the inner surfaces 163 and 164 ofthe first and second openings 161 and 162 can extend at any constant orvariable angle relative to the major surface 121.

Although not shown, a dielectric layer can optionally be formed on themajor surface 121 of the substrate 120 and/or overlying the innersurfaces 163 and 164 of the first and second openings 161 and 162 toprovide electrical isolation of the conductive elements 140 a and 140 band the conductive vias 170 from the substrate. Such a dielectric layercan be formed using any of the various methods described above withreference to the dielectric layer 25 shown in FIG. 2B. Such a dielectriclayer can be in addition of or instead of a passivation layer that mayalready be overlying the major surface 121 of the substrates 120.

In the stage of fabrication illustrated in FIG. 4B, the anchor portions141 a and 141 b and the respective connecting portions 145 a and 145 bof the conductive elements 140 a and 140 b can be formed within thefirst openings 161, the joining portions 142 a and 142 b can be formedoverlying the major surface 121, and the conductive vias 170 can beformed within the second openings 162, with the contact portion 180exposed at the second surface 122. Each of the anchor portions 141 a and141 b, the connecting portions 145 a and 145 b, the joining portions 142a and 142 b, and the conductive vias 170 can be formed in a single metaldeposition process or separate processes. In an embodiment where theconductive vias 170 are electrically coupled to separate conductivecontacts exposed at the second surface 122, such conductive contacts canbe formed in a single metal deposition process along with the conductiveelements 140 a and 140 b and the conductive vias, or such conductivecontacts can be formed in a separate process.

An exemplary method of forming the conductive elements 140 a and 140 band the conductive vias 170 involves depositing a metal layer by one ormore of sputtering a primary metal layer onto exposed surfaces of thesubstrate 120, plating, or mechanical deposition. Mechanical depositioncan involve the directing a stream of heated metal particles at highspeed onto the surface to be coated. This step can be performed byblanket deposition onto the major surface 121 and the inner surfaces 163and 164, for example. In one embodiment, the primary metal layerincludes or consists essentially of aluminum. In another particularembodiment, the primary metal layer includes or consists essentially ofcopper. In yet another embodiment, the primary metal layer includes orconsists essentially of titanium. One or more other exemplary metals canbe used in a process to form the conductive elements 140 a and 140 b andthe conductive vias 170. In particular examples, a stack including aplurality of metal layers can be formed on one or more of theafore-mentioned surfaces. For example, such stacked metal layers caninclude a layer of titanium followed by a layer of copper overlying thetitanium (Ti—Cu), a layer of nickel followed by a layer of copperoverlying the nickel layer (Ni—Cu), a stack of nickel-titanium-copper(Ni—Ti—Cu) provided in similar manner, or a stack of nickel-vanadium(Ni—V), for example.

In a particular embodiment, the joining portions 142 a and 142 b can bedeposited onto the major surface 121 of the substrate 120 beforeremoving any material from the substrate, for example, as shown in thestage of fabrication illustrated in FIG. 2A. In such an embodiment, theholes 160 can be formed, for example, by etching through the joiningportions 142 a and/or 142 b and then etching into the substrate 120.After the holes 160 are formed through the joining portions 142 a and/or142 b, the connecting portions 145 a and 145 b, the anchor portions 141a and 141 b, and the conductive vias 170 can be formed as describedabove.

In the stage of fabrication illustrated in FIG. 4C, the dielectric layer125 is formed on the major surface 121 of the substrate 120 and servesas an etch mask layer where it is desired to preserve remaining portionsof the major surface. The dielectric layer 125 can be formed using anyof the various methods described above with reference to the dielectriclayer 25 shown in FIG. 2B. The joining portions 142 a and 142 b canremain at least partially exposed at the major surface 121 (i.e., notcovered by the dielectric layer 125) for connection to a componentexternal to the first microelectronic unit 112.

Thereafter, in the stage of fabrication illustrated in FIG. 4D, therecesses 130 can be formed in a similar manner and using similarprocesses as described above with respect to forming the recess 30. Forexample, the recesses 130 can be formed by selectively etching thesubstrate 120 to remove material of the substrate, after forming a masklayer (e.g., the dielectric layer 25) where it is desired to preserveremaining portions of the major surface 121. The recess 130 can beformed such that material of the substrate 120 supporting at least thejoining portions 142 a and 142 b is removed. Similar to the recess 30,the inner surfaces 131 of the recesses 130 can extend at any constant orvariable angle relative to the major surface 121.

As shown in FIG. 4D, the recesses 130 can be formed such that they donot extend as far from the major surface 121 as the first openings 161,such that contours of the anchor portions 141 a and 141 b conform to acontour of the remaining part of the inner surface 163 of the firstopening. In a particular embodiment, the recesses 130 can be formed suchthat they extend at least as far from the major surface 121 as the firstopenings 121, such that the contours of the anchor portions 141 a and141 b do not conform to contours of any inner surfaces of the substrate120. In such an embodiment, the anchor portions 141 a and 141 b can befixed to the substrate 120 through the attachment between the anchorportions and the conductive vias 170 that can have contours that conformto contours of the inner surfaces 164 of the second openings 162.

Thereafter, in the stage of fabrication illustrated in FIG. 4E, thedielectric regions 150 can be formed inside the recesses 130 in asimilar manner and using similar processes as described above withrespect to forming the dielectric region 50 inside the recess 30. Forexample, the dielectric region 150 can be formed such that an exposedouter surface 151 of the region is co-planar or substantially co-planarwith the major surface 121 of the substrate 120 (as shown in FIG. 4E) oran exposed surface of the dielectric layer 125.

Thereafter, referring again to FIG. 3A, the first microelectronic unit112 can be stacked on top of the second microelectronic unit 114,thereby forming the stacked microelectronic assembly 110. As describedabove, connection between the first microelectronic unit 112 and thesecond microelectronic unit 114 can be through conductive masses 118.The conductive masses 118 can provide an electrical connection betweenthe joining portions 142 a and 142 b of the first microelectronic unit112 and the conductive contacts 16 of the second microelectronic unit114. In such arrangement, the joining portions 142 a and 142 b arealigned with the respective conductive contacts 16.

As shown in FIG. 5, a base portion 241 and a joining portion 242 of aconductive element 240 is shown that is suitable for use in any of theembodiments described above with reference to FIGS. 1A-4E. The joiningportion 242 extends from the base portion 241 of the conductive element240. The base portion 241 can be, for example, part of the joiningportion 142 a or 142 b described above with reference to the firstmicroelectronic unit 112 shown in FIG. 3A, or part of the anchor portion41 described above with reference to the first microelectronic unit 12shown in FIG. 1A. The base portion 241 can be connected to otherconductive elements located beneath the major surface 221 of thesubstrate 220 or beneath an outer surface 251 of the dielectric region250. In the embodiment shown in FIG. 5, the base portion 241 includes asegment 243 that is compliant or movable in a direction of a platedefined by the major surface 221, such that the segment is capable ofbeing displaced in a direction along the major surface 221 by anexternal load applied thereto.

Referring now to FIG. 6, a first microelectronic assembly 12′ accordingto another embodiment is similar to the first microelectronic assembly12 shown in FIG. 1A, except that the conductive elements 40′ areelectrically connected to conductive vias 70 a and 70 b extendingbetween the major surface 21 and the second surface 22 of the substrate20′.

The substrate 20′ includes holes 60 a and 60 b extending from the majorsurface 21 and the second surface 22, and the conductive vias 70 a and70 b extend within the respective holes from respective anchor portions41′ of the conductive elements 40′ to the second surface. Eachconductive via 70 a and 70 b includes a contact portion 80 exposed atthe second surface 22 for interconnection with a component external tothe first microelectronic unit 12′. The hole 60 a is a staged holesimilar to the holes 160 shown in FIG. 3A, except that the openings 30do not overlap with either of the holes 60 a or 60 b, so the holes 60 aand 60 b extend from the second surface 22 to the major surface 21,rather than from the second surface to a respective opening. The hole 60b is not staged, i.e., the hole 60 b can be formed, for example, in asingle etching or other process of removing material from the substrate20′.

Similar to the first microelectronic assembly 12 shown in FIG. 1A, eachconductive element 40 includes a joining portion 42 that can be exposedat the major surface 21 for interconnection with a component external tothe first microelectronic element 12′. Also similar to the firstmicroelectronic assembly 12, the dielectric regions 50 can be compliant,such that each joining portion 42 can be movable relative to thesubstrate 20′.

FIG. 7 depicts a module 300 including at least two microelectronicassemblies 310 arranged together in one unit having an electricalinterface 320 for transport of signals to and from each of themicroelectronic assemblies 310. The electrical interface can include oneor more contacts usable for transport of signals or referencepotentials, e.g., power and ground, which are common to each of themicroelectronic elements therein. The microelectronic assemblies 310 maybe any of the assemblies described above. In a particular example, themodule 300 can be a dual in-line memory module (“DIMM”) or singlein-line memory module (“SIMM”) having one or more portions thereof sizedfor insertion into a corresponding slot of other connector of a system,such as can be provided on a motherboard. In such DIMM or SIMM, theelectrical interface can have contacts 330 that are suitable for matingwith a plurality of corresponding spring contacts within such slotconnector. Such spring contacts can be disposed on single or multiplesides of each slot to mate with corresponding module contacts. Variousother modules and interconnection arrangements are possible in which amodule may have unstacked or stacked microelectronic assemblies, orwhich may have parallel or serial electrical interfaces, or acombination of parallel and serial electrical interfaces for transportof electrical signals to and from the module. Any kind of electricalinterconnection arrangement between the module 300 and a further systeminterface is contemplated by the invention.

The microelectronic assemblies described above can be utilized inconstruction of diverse electronic systems, as shown in FIG. 8. Forexample, a system 400 in accordance with a further embodiment of theinvention includes a microelectronic assembly 406 as described above inconjunction with other electronic components 408 and 410. In the exampledepicted, component 408 is a semiconductor chip whereas component 410 isa display screen, but any other components can be used. Of course,although only two additional components are depicted in FIG. 8 forclarity of illustration, the system may include any number of suchcomponents. The microelectronic assembly 406 may be any of theassemblies described above. In a further variant, any number of suchmicroelectronic assemblies may be used.

Microelectronic assembly 406 and components 408 and 410 are mounted in acommon housing 401, schematically depicted in broken lines, and areelectrically interconnected with one another as necessary to form thedesired circuit. In the exemplary system shown, the system includes acircuit panel 402 such as a flexible printed circuit board, and thecircuit panel includes numerous conductors 404, of which only one isdepicted in FIG. 8, interconnecting the components with one another.However, this is merely exemplary; any suitable structure for makingelectrical connections can be used.

The housing 401 is depicted as a portable housing of the type usable,for example, in a cellular telephone or personal digital assistant, andscreen 410 is exposed at the surface of the housing. Where structure 406includes a light-sensitive element such as an imaging chip, a lens 411or other optical device also may be provided for routing light to thestructure. Again, the simplified system shown in FIG. 8 is merelyexemplary; other systems, including systems commonly regarded as fixedstructures, such as desktop computers, routers and the like can be madeusing the structures discussed above.

The vias and via conductors disclosed herein can be formed by processessuch as those disclosed in greater detail in the co-pending, commonlyassigned U.S. patent application Ser. Nos. 12/842,587, 12/842,612,12/842,651, 12/842,669, 12/842,692, and 12/842,717, filed Jul. 23, 2010,and in published U.S. Patent Application Publication No. 2008/0246136,the disclosures of which are incorporated by reference herein.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

It will be appreciated that the various dependent claims and thefeatures set forth therein can be combined in different ways thanpresented in the initial claims. It will also be appreciated that thefeatures described in connection with individual embodiments may beshared with others of the described embodiments.

1. A method of fabricating a microelectronic unit, comprising: removingmaterial from a substrate having a CTE less than 10 ppm/° C. to form ahole extending from a major surface of the substrate to a second surfaceopposite the major surface; forming an electrically conductive elementhaving a joining portion extending above and supported on the majorsurface, an anchor portion fixed relative to the substrate, and aconnecting portion extending downwardly from the joining portion to theanchor portion, a surface of the connecting portion having a contourconforming to a contour of an inner surface of the hole; removingmaterial supporting at least a joining portion of the conductive elementfrom the major surface to form a recess such that the joining portion atleast partially overlies the recess, and such that the contour of thesurface of the connecting portion does not conform to a contour of aninner surface of the recess; and depositing a material within the recesshaving a modulus of elasticity less than 10 GPa, wherein the joiningportion is at least partially exposed at the major surface of thesubstrate for connection to a component external to the microelectronicunit.
 2. The method as claimed in claim 1, wherein the substrate has aCTE less than 7 ppm/° C.
 3. The method as claimed in claim 1, furthercomprising, before the step of forming the conductive element, forming aconductive via extending within the hole and extending towards thesecond surface, such that the step of forming the conductive elementelectrically couples the conductive element with the conductive via. 4.The method as claimed in claim 1, wherein the step of forming theconductive element is performed such that the joining portion isnon-centered relative to the connecting portion.
 5. The method asclaimed in claim 1, wherein the step of forming the conductive elementis performed such that the joining portion is disposed substantiallyparallel to the major surface.
 6. The method as claimed in claim 1,wherein the substrate consists essentially of one material selected fromthe group consisting of: semiconductor, glass, and ceramic.
 7. Themethod as claimed in claim 1, wherein the substrate includes a pluralityof active semiconductor devices, and the step of forming the conductiveelement electrically connects the conductive element with at least oneof the plurality of active semiconductor devices.
 8. The method asclaimed in claim 1, wherein the step of forming the conductive elementis performed such that the joining portion defines an internal aperture.9. The method as claimed in claim 8, wherein the step of forming theconductive element is performed such that the aperture extends throughthe joining portion into the connecting portion.
 10. The method asclaimed in claim 9, further comprising depositing a dielectric materialinto at least a portion of the aperture.
 11. The method as claimed inclaim 1, wherein the step of removing material from the substrate toform a hole includes forming a first opening extending from the majorsurface towards the second surface and a second opening extending fromthe first opening to the second surface, wherein inner surfaces of thefirst and second openings extend in first and second directions relativeto the major surface, respectively, to define a substantial angle.
 12. Amethod of fabricating a stacked assembly including at least first andsecond microelectronic units, the first microelectronic unit beingfabricated as claimed in claim 1, further comprising the step ofelectrically connecting the substrate of the first microelectronic unitto a substrate of the second microelectronic unit.